Electric incandescent lamp and method of manufacturing



June 1951 R. K. BRAUNSDORFF 2,556,0

ELECTRIC INCANDESCENT LAMP AND METHOD OF MANUFACTURING Filed June 21, 1949 2 Sheets-Sheet l i/ Hi1 W 6210M m M ATTORN EYS J1me 1951 R. K. BRAUNSDORFF 2,556,059

ELECTRIC INCANDESCENT LAMP AND METHOD OF MANUFACTURING Filed June 21, 1949 2 Sheets-Sheet 2 ATTORN EYS Patented June 5, 1951 ELECTRIC INCANDESCENT LAMP AND METHOD OF MANUFACTURING Reginald K. Braunsdorfi, East Orange, N. J., as-

signor to Tang-Sol Lamp Works, Inc., Newark, N. J a corporation of Delaware Application June 21, 1949, Serial No. 100,332

Claims. 1

This invention relates to electric lamps and particularly to miniature incandescent lamps for automotive purposes, although certain features thereof are of utility in other applications.

An object of the invention is a new and improved lamp construction wherein shorter light center lengths can be obtained.

Another object is a new and improved lamp of the character set forth wherein limitations on the diameter of the leading-in Wires are, for all practical purposes, eliminated and a single piece, straight-through leading-in wire construction may be used.

Still another object of the invention is a novel and improved miniature incandescent lamp which is characterized, among other things, by the low cost of manufacture thereof as compared with the cost of manufacturing conventional lamps.

A further object of the invention is a method of manufacturing such miniature lamps which is characterized by the low cost of manufacture and further by the production of lamps of more uniformly good quality with fewer rejects.

Other objects of the invention will hereinafter appear.

For a better understanding of the invention reference may be had to the accompanying drawings, wherein Fig. 1 is a diagrammatic view of an exploded view of a bulb and a mount therefor embodying the invention;

, Fig. 2 is a side view of the completed lamp with parts broken away;

Fig. 3 is an exploded view similar to Fig. 1 of another embodiment;

Fig. 4 is a side view of the completed lamp of the embodiment of Fig. 3;

Fig. 5 is an exploded view of the mount parts of a lamp embodying the invention;

Fig. 6 is a diagrammatic view partly in section of the completed mount of Fig. 5;

Fig. 7 is a side view of another embodiment of the invention;

Figs. 8a, 8b, 8c and 8d are enlarged diagrammatic views illustrating certain steps in the manufacture of the embodiment of Fig. '7;

Fig. 9 is a sectional view of another embodiment of the invention;

Fig. 10 is a side view of another embodiment of the invention;

Fig. 11 is an enlarged view of the embodiment of a part of the lamp of Fig. 10;

Fig. 12 is a View partly in section of the button element utilized in the embodiment of Fig. 10

Fig. 13 is an exploded view of a miniature photo flash lamp bulb embodying the invention;

Fig. 14 is a diagrammatic side View partly in section of the embodiment of Fig. 13;

Fig. 15 is an exploded view of an envelope and a button mount for a radio tube embodying the invention; and

Fig. 16 is a side view partly in section thereof.

Referring to Figs. 1 to 4, inclusive, I have illustrated my invention as embodied in conventional automotive head or projector lamp bulbs. The lamp or bulb of Figs. 1 and 2 is one conventional type and shape and the lamp or bulb of Figs. 3 and 4 is of another conventional type. The lamp of Figs. 1 and 2 is a multiple filament lamp while the lamp of Figs. 3 and 4 is a single filament lamp.

It is conventional practice in making these automotive lamps to form mount stems comprising flares and then to fuse the flares and necks of the bulbs together. Conventional bases are then attached to the neck of the bulb. This practice involves the utilization of fusing temperatures high enough to melt the glass of the bulb neck and the flare and this gives rise to special annealing and other problems. Also in the manufacture of the stems the fiares are melted upon the lead wires and special lead wires are required, as for example, of Dumet wire which are limited as to the volume of current that may be employed. By the invention illustrated in Figs. 1 to 6 this conventional practice with its special problems and expensive operations is avoided.

Referring to Figs. 5 and 6 I first form a mount of the simplified character shown in these figures which comprises simple metallic lead wires I, a disc 2 of glass and a conventional lighting filament 3. The disc 2 is provided with apertures or holes 4, one for each of the metallic wires I and these metallic wires 1 are fastenedto the disc or button '2 and sealed within the openings 4 by means of a suitable bonding material 5 which melts or fuses at a temperature substantially below the fusing temperature of the glass of the button or disc 2. 5 should also have a coefficient of expansion approaching that of the glass disc 2 but as indicated should melt at a substantially lower tem perature so that the bonding material can be fused into the openings 4 about the metallic lead wires I without fusing the button or disc 2 at any point thereof and without setting up undue strains therein. In the particular embodiment illustrated the bond 5 is formed by first forming about the leads I a mass 5' of such material at The bonding material 2 is provided with such a material I I.

3 the desired points thereof. This is effected by first mounting on the lead wires I cross lengths 6, these cross lengths 6 being fastened to the lead wires I at points which are desired to be at or substantially flush with the inner face of the disc or button 2. After these short cross lengths 6 are fastened the bonding material 5 is anchored to the length 6, as by heating sufficiently to anchor it and as diagrammatically shown in Fig. 5 this bonding material forms a bead-like body after it has been thus anchored to the cross wires at this point. With the metallic lead wires I thus provided with the beads or globules of bonding material 5 and with the filaments 3 mounted on the ends thereof in any conventional manner these lead-in wires l and the button or disc 2 are then assembled with the lower ends of the lead wires I passing through the openings 4 of the button, and with the globules or masses 5 of fusing material restthe masses of bonding material 5' are heated to a temperature sufficient to fuse them about the lead wires I and in the openings 5 as shown in Fig. 6. Since the fusing temperature of the bonding material is substantially below that of the glass of the button or disc 2 the heating of the-disc or button 2 is substantially less than is required to fuse it and the annealing and other probles arising at the higher temperatures are avoided and wires I are of sufficient capacity to carry the load without limitation. After the making of the simple mount of Fig. 6 it is then assembled into the bulb and bonded thereto as described below.

The disc or button 2 is formed with an upper flat surface 2' at its periphery for assuming an abutting relation with the end of the neck of a bulb and the upper central part of the disc or button is slightly tapered in an upward direction as indicated at l and extends into the inside of the neck of the bulb.

The button or disc is provided also with an aperture 8 which may conveniently be centrally "disposed of thebutton or disc for the reception of an exhaust tube 9. The latter is preferably of glass and is also preferably fastened within the opening 8 by means of a bonding material similar to the bonding material 5, namely one which has a fusing or melting temperature substantially below that of the button or disc 2' and the exhaust tube 9 and also preferably having a coefficient of expansion approximating the coefficient of expansion of the glass.

With the button or disc mount shown'in Fig. 6 thus formed it is then assembled into fastening and sealing relation with the bulb I0 shown in Figs. 3 and 4. Before the bulb II! and the button or disc mount are assembled one of these elements is provided at the sealing line with a suitable bonding material which fuses at a temperature substantially below the fusing temperature of the envelope or bulb It] and in the particular embodiment shown the disc or' button This bonding material II is positioned on the upper surface 2' of the disc and around the tapering upper part I of the disc. The two elements are then assembled with the abutting edge It of the neck of the bulb III resting upon the material 'I I" and with the upper tapering part of the disc or button projecting into the neck of the bulb. With the parts thus assembled sufficient heat is applied to the bonding material II, to fuse the neck of the bulb to the button or disc. This sealing in the particular embodiment shown comvelope I'D.

prises both a butt seal between the abutting edge Ill of the neck of the bulb Ill and the upper surface 2 of the button or disc 2 and also a seal around the inner edge of the neck of the bulb Ill to the lower part of the taper I. The bond thus formed is indicated at I l in Fig. 4. By thus sealing thebutton or disc mount to the neck of the bulb II], the highest temperature to which any part of the bulb I8 and the button or disc 2 is subjected is the fusing temperature of the bonding material II and since that is substantially below the fusing temperature of the bulb and the disc the annealing and other problems are simplified and the stress and strains are minimized during the sealing-in step. 7

The embodimentof Figs. 1 and 2 is the same as that of Figs. 3 and 4, the only difference being that a differently shaped bulb or envelope I2 is used and multiple filaments 3 are employed requiring more than two leads I.

In Figs. 2 and 4 the lamps have been exhausted or filled with the desired gas and the exhaust tubes 9 are sealed off as indicated at 9'.

Instead of forming the mount and assembling the mount in two steps, this may be done in a single step, that is before the lead wires I are actually fastened to and sealed to the button 2 the assembly consisting of the button, the leads 9 and the bulb ID (or I2) are assembled together in the desired sealing relationship and the assembly is then heated to a temperature sufiicient to fuse the bonding materials 5' and II simultaneously which temperature is below the fusing temperature of the button and the en- This heating may, for example, be effected by heating the whole assembly in an oven or the heating may be effected in any other suitable manner as, for example, by applying gas burner flames thereto or to the neck and disc. The heating which is sufficient to fuse the bonding material and seal the parts together may be effected in a very short time as, for example, a period of a minute or substantially less than a minute. Thus where in the conventional practice two separate heating operations are required, namely one for making the conventional stem and second the fusing of the stem to the glass bulb, I am able to form th completed bulb with just one heating except for the exhaust and sealing off operation. This latter operation may be efiected immediately after the sealing of the leads I, the buttons 2 and the bulbs together so as to avoid cooling and reheating for the exhaust. However, the sealing and fastening of the exhaust tube 9 to the button 2 may be effected at the same time, namely simultaneously with the fusing of the bonding materials 5 and II.

The lead wires I as above indicated may be the plain conventional alloy wire used as the support wires in conventional automotive lamp bulbs and no special sealing-in wire as, for ex ample, Dumet is required. The cross wires '6 may be of the same alloy as the lead Wires I and these wires function to facilitate the anchoring of the bonding material thereto and to prevent the wires I from tending to slide 'relatively to the button'2 during the sealing step.

The bonding material ii and II may be of paste form or of solid form. The solid form may be formed into a ring I! and disposed on the surface 2' of the button 2 or the material in the form of a paste mayube applied to 2', and similarly with respect to the 5 bonding material 5. The glass of the bulbs l and I2 may be of the conventional lime or lead glass and similarly the buttons 2 and the exhaust tubing 9 may be of the same glass. Any suitable bonding material may be used for the material 5' and II having a fusing temperature substantially below the softening or fusing temperature of soft glass of which the bulbs I?) and [2, the button 2 and the exhaust tube 9 are formed. It must have the quality of forming a firm bond between the elements with a tensile strength sufficient to hold the parts firmly united and other desired characteristics such as freedom from crazing. It also must have a coefficient of expansion in the neighborhood of the coefficient of expansion of the soft glass parts which are to be sealed and bonded together. I have obtained particularly good results by utilizing a low fusing material which may be described generally as of the lead or lead oxide family of such materials available on the market. For example, I have obtained good results with a bonding material containing 50% or more of lead or lead. oxide and a suitable flux or fluxes and a suitable filler or fillers to compensate for any irregularity in the expansion of the flux of mass when fused and set between and to the button surfaces of the elements to be sealed and joined. The elasticity of the fillers compensates for any irregularity in the expansion of the flux or mass when fused and set between and to the surfaces. It has a coemcient of expansion in the neighborhood of the coefficient of expansion of lime glass and has a range of expansion coefficient of from 85 to 95 multiplied by It melts or fuses at a temperature under or around 500 C. which is substantially below the softening or melting point of lead. glass, which is roughly 626 C and that of lime glass which is roughly 696 C. This bonding and sealing ma terial when fused between the juxtaposed surfaces of the peripheral edges forms a firm union between the soft glass elements to be joined which has been demonstrated by tests to be at least as strong, if not stronger than the glass itself and further the bonding and sealing operation may be effected with little or no rejects or shrinkage. This fused bonding material appears to merge into and in effect form part of the glass of the elements to be joined notwithstanding the fact that the bonding operation is carried on at a temperature well below the fusing temperature of the glass elements to be joined and with the film or layer of bond having tensile strength adequate not only to firmly unite the elements when the lamp is evacuated but also when. the lamp is pressurized with gas. It is understood however that my invention is not limited to this particular bonding material since other bonding materials having characteristics of the above described bonding material may be utilized.

In the embodiments of Figs. 7 and 8 the leadin wires are in the form of tubes and these tubular conductors are sealed in openings formed in the buttons IS in a manner similar to the sealing of the lead wires i into the button 2 as above described and by the use of a bonding material similar to the bonding material 5, 5' of Figs. 1 to 6. The filament l! is mounted upon support wires is of conventional metal as, for example, nickel alloy, with their lower ends fastened to the inner ends of the tubular conductors l5, as, for example, by welding. The button 16 is bonded to the neck of the bulb I9 by means of a bonding material similar to the bonding material ll of Figs. 1 to 4 and in a similar manher, this bonding material having a fusin point substantially below the fusing point of the glass of the button It and the bulb If). The hollow conductors or lead wires 15 are utilized for flushin the air out of the bulb l9 and for introducing any desired gas inside the bulb. Figs. 8a to 8d are enlarged views of the neck portion of the bulb It for purposes of illustration. A pinch is formed in the side of one tubular conductor it which is to be used as the inlet, this pinch 20 being formed adjacent thebutton I6. Into the outer end of this tube It is placed a sealing and bonding material which may be similar to the bonding material 5 and H above described or any other suitable material. In the particular embodiment shown this bonding material 2| is in the form of an elongated body which is inserted in the open end of the tube up against the walls of the pinch 20. A pinch 22 is also formed in the other tubular conductor 15 but before this pinch is formed a body of sealing and bonding material 25 is inserted in the open end of the tube beyond the point where the pinch 22 is to be formed and then the latter is formed, or the material 2| may be inserted into the inner end of the tube 15 after the pinch 22 is formed and before the mount is sealed to the bulb, but in scaling in the mount care must be taken not to fuse the material 2|. This latter tubular conductor I5 forms the outlet through which the air and other gaseous material to be removed from the tube is flushed. A flushing gas is then introduced into the inlet tube as, for example, by connecting a rubber tube to the inlet which tube is connected with the source of flushing gas pressure. After the bulb I9 is flushed the sealing material 2! is heated and melted to seal up the outlet tubular conductor at the pinch 22. This heating may be effected by the flame as shown in Fig. 8b. The supply of flushing gas is preferably continued while this bonding and sealing material 2! is being fused to close the outer tube at the pinch 22. After the bulb is flushed out in this manner and the outlet tube sealed at the pinch 22, the pressure of the gas can be increased and raised to the desired value inside the bulb. When this is effected, the body or fusing material 2| below the pinch 29 is fused or melted so as to seal the inlet tube (Fig. After the fusing of the sealing material Zl, the outer ends of both the inlet and outlet tubular conductors may be filled with lead solder melted thereinto as indicated at 25 in Fig. 8d. The heating flame may be of an ordinary gas and air flame for heating and fusing the bonding and sealing bodies 2i, and Argon gas may be used as the flushing gas. By forcing the Argon gas through the inlet tubular conductor, the air therein and other gases are forced out through the tubular outlet past the pinch 22 and when the gas is all out the outlet tubular conductor is sealed as described above, whereupon the Argon gas is continued to be supplied until the desired pressure is reached. Some of the Ar-gon gas is likely to be lost in this operation of flushing, and therefore a less expensive gas such as hydrogen maybe used as the principal flushing medium. After the air is' flushed out of the bulb, the Argon is supplied through the inlet to drive out the hydrogen, or the greater portion of it, whereupon the outlet tube is sealed and the Argon gas continued to be supplied up to the desired pressure.

The tubular lead-in structure illustrated in. the embodiment of Figs. 7 and 8 may be used for connection directly to an external circuit, and thus eliminate the conventional lamp base; this would result in a material reduction in the cost of the lamp. This is also true of the embodi-v ment illustrated in 9, wherein concentric tubular terminals sealed into the glass. envelope are employed.

In flushing the lamps having the tubular-type terminals. as. illustrated in Figs. 7 and 8, it is possible to. eiiect the flushing operation without the need for conventional pumping. By the combination of an adequate flush plus heating of the filament in a. controlled flush atmosphere, such as, for example, hydrogen, the envelope could be thoroughly purged residual gases and filled with an] inert gas such asargon, for example. Moreover, with this particular lamp construction it is. possible to employ filling pressures up to the bursting strength of the assembled parts, and the, lamps could be tipped off with pressures of the order of several atmospheres and even higher. For instance, the plug Zlcould be melted within its terr'linal I5 while the gas pressure is being maintained on the lamp, since the pressures on eitherlside. of. the pl s would; be qual, and an effective seal could be made.

With this structure, as well as with the structures previously described, short light-center lengths are readilyatjtainable, and this is particularly so where the lezuiing-in wires form the terminals to connect the lamp directly to an external circuit without the necessity for a conventional as facilitates the positioning of filaments in what are generally termed pie-focused lamps, and in which the filament must occupy a predetermined position with respect to the base or some other guiding feature on the bulb, so that when it is mounted in the apparatus, the filament will be in a predetermined position with respect to the optical System with which it is to cooperate. Morcoye'r, by means of the greatly decreased light center lengths available with the structure as illustrated in Figs. 7 and 8, as well as with other embodiments of the invention illustrated in the drawings, far greater latitude is permissible in the design .of associated optical devices than would be permissible with conventional lamp structures with which I am familiar.

In the embodiment of 9 I have shown a conventional type of bulb Sr) with the filament mount comprising concentric tubular leadwin conductors, these concentric conductors comprising an outer hollow or tubular conductor 3% and an inner tubular conductor 32. These two tubular conductors 3i and 32 may be insulated from each other in any suitable manner but preferably th y are insulated from each other and fastened firm :ly together by means of an insulating and bonding material 33 of the character of the bonding material 5', ii and 2t above described. This bond is fused or melted in situ in a manner to surround the inner tube 32 and to bond the latter to the outer tubular conductor 3! in substantially concentric relation therewith. A con venticnal filament 34 is mounted on filament support wires 35 and 323, the support wire 35 being fastened to the outer tubularconductor 3i by weldin and the support wire 35 being fastened similarly to the upper end of the inner tubular conductor 32, the latter projecting slightly beyond the inner end of the outer tubular conductor 3! to facilitate the welding of the sup Moreover, this structure greatly tors 3| and 32 is inserted and the two parts are fastened, and sealed together along the pet riphery of the opening of the flare 3?, as shown at 38 the latter prefer-ably being a bond material of; the character of the bond material II and. 2!, above described. I-he flaring periphery of the flare fl is also, fastened and sealed into the necl; of the bulb neck 3!) of the bulb 39 by means of the bonding material 39 which is similar to the bonding material 38. Both the seals 33 and 39 may be formed simultaneously or the seal at 38 may be first formed and the seal at formed thereafter. The inner tubular lead-in conductor 32 is utilized for enhausting the lamp and for introducing a suitable gas if desired. At the completion of the exhaust the tubular con: ductor 3.2 is closed off in any suitable manner and I have indicated it as closed oil by a sealing material at; which may be of the character of the bond and seals 38 and 3,9. The tubular conductors 3i and 32 may be of a conventional alloy Known in the trade as No. 4 alloy. The seals 33, Ill; and 39 may be formed simultaneously so as to avoid reheating in steps if they are formed at different times.

Firm and secure bonds and sealsv are thus ob tained between the tubular lead-in conductors 3i, and 32, between the tubular conductor 3! and the flare 3i and between the flare and the neck 30' of the bulb 3i) and moreover without heating either the flare 3-: or the bulb 3.0 to the fusing or melting point. The low working temperatures simplify the bonding and sealing operation as well as annealing operations and the mount structure is considerably simplified. This pro: vides a complete single circuit lamp with only one protruding connector which then itself is in sulated to provide the circuit connections. The lamp of this embodiment is particularly adapted for use with a special type jet connector.

In the embodiment of Figs. 1,0, 11 and 12 I have illustrated a bulb of a conventional type and shape and having the lead-in wires 5! fastened and sealed in position by being embodied in the bond and seal 52 formed between the button closure 53 and the neck 50 of the bulb 50. The button closure 53 is formed by flaring the exhaust tube 54 at one end. This flare '53 is provided with V notches 55 on its periphery tor 1e accommodation of the lead-in conductors 5| and the bonding material 52 utilized in bonding and sealing the flare 5 3 to the neck 50' at the same time bonds and seals the conductors 5! in these V notches. This bonding material 52 is of the character of the bonding materials 5', .H and 21 above described, reg ment ShQ th lead-in c nd 5' are offset at 5! to accommodate them to the sealing position between the periphery of the fla1'e 53 and the neck 58 of the bulb and at the same time to be in a position to support the filament :56 in the desired manner. All parts are jigged in the final position and oven-heated to efifct the seals. The exhaust is eifected through the exhaust tube 54 and the latter "is sealed off in any conventional manner at 54. This provides a simple and inexpensive construction for low cost lanips such as photoflash or other surfaces where a special connector may be provided. t

In the particular em- In the embodiment of Fig. 14 I have illustrated a photoflash lamp comprising a bulb 60 and a button mount 6|. The latter is similar to the button mount 2 described above with respect to Figs. 1 to 6 and is bonded and sealed to the neck of the bulb 60 by means of a bonding material I 1 identical with that described with respect to Figs. 1 to 6. This bonding material H when fused forms the bond l I of Fig. 14.

The lead-in conductors 62 are sealed into the button 6| in the manner similar to the sealing of the lead-in conductors l to the button '2 of Figs. 1 to 6, namely, by the use of a bonding material similar to the bonding material and II. An exhaust tube 63 similar to the exhaust tube 9 of Figs. 1 to 6 is bonded and sealed to the button 6| and in the manner described above with respect to exhaust tube 9. The conductors 62 carry an igniting filament 64 for igniting the magnesium or aluminum foil 65 contained in the bulb 6. The ignition means and the magnesium or aluminum foil are of any conventional structure and as in conventional practice oxygen is contained in the bulb 60 to accelerate the lighting flare. Fig. 13 is an exploded view of the bulb 60 and the mount before the mount and the bulb are bonded and sealed together, the bonding material H being positioned about the button BI either in the paste or solid form.

In the embodiment of Figs. 15 and 16 I have illustrated a radio tube having an envelope 10 and a button mount H, the interior structure of the radio tube being omitted for convenience in illustration. The mount ll comprises a button '12 similar to the button 2 of Figs. 1 to 6. The open end of the tube in is butt sealed and bonded to the button 12 in a manner similar to the sealing and bonding of the button 2 to the neck of the bulb l2 above described and by the use of a bonding material ll similar to the bonding material H of Figs. 1 to 6. The mount II also comprises a multiplicity of terminal connectors 73 which are conventional. These terminal connectors may be sealed into the button during the button molding process, or they may be secured in the button in substantially the same manner as shown and described in connection with Figs. 5 and 6.

With the new and improved lamp construction as previously described, applicant is able to form incandescent lamps having much shorter lightcenter lengths, which feature is of great importance in certain applications, and especially in applications wherein the filament is to be disposed at a particular point with respect to a reflector.

Another important and outstanding advantage of this invention resides in the particular leading-in wire structure. With conventional methods of sealing in the leading-in wires in incandescent lamps with which I am familiar, the diameter of the wire is limited, since too large a wire will crack the press supporting the Wires and filament, and this wire limitation limits the amount of power that can be delivered to the filament. With applicants construction, however, there is, for all practical purposes, no limitation whatever on the Wire size, and relatively large wire diameters may be employed without any possibility of cracking or otherwise damaging the button part of the lamp even in the presence of the wide temperature range encountered during normal use of lamps of this type.

Furthermore, the use of the button seal and leading-in wire construction in accordance with 10 this invention enables the use of a straight single section of leading-in wire, which materially reduces the cost of manufacturing the lamp as compared with the three-piece leading-in. wires used in conventional lamp constructions with which I am familiar.

For the sealing material denoted by the numeral H in the drawings, as for instance in Fig. 1, and the sealing material denoted by 5 and 5' in Figs. 5 and 6, for instance, I have had particularly good results by utilizing a low fusing material which can be described generally as being of the lead or lead oxide family of such materials available onthe market. Although it is understood that other bonding materials having the same characteristics may be used, as for example the bonding material previously described, they should preferably have a temperature coeffijcient of expansion around or fairly close to glass, namely a coefficient of expansion of to 94 l0 The bonding material previously described has a softening point below 450 C. (around 415 C. to 420 C.) and it melts or fuses at a temperature around 500 C. Its fluidity becomes quite marked at temperatures above 500 C. This marked fluidity of the bonding material is such that when a portion thereof in the pulverized or granular form is positioned on a glass slide and heated to the fusing and melting temperature, it tends to flow into a thin layer and when heated to above 500 C., as for example to 575 C., say for fifteen minutes, it flows very thin and spreads itself in a very thin flat layer on the slide. I believe this tendency of the fused bonding material to spread into a thin layer or film at around or above 500 C. is important in the forming of the seal and strong rigid joint, although I have obtained fairly good results with bonding materials whose fluidity at the fusing and melting temperature is substantially less than that of the specific bonding material described above.

Any suitable glass may used for the bulb and button parts, such for example as lead glass which softens at around 626 C., and lime glass which. softens at around 696 C., and by softening is meant softening to a point where the glass becomes slightly flexible or distortable from its shape, or begins to become flexible or distortable.

I have had particularly good results by using bulb and button parts made of lime glass.

The temperature coefficient of expansion of lead glass at 0 0-810 '0. is around 90X 10 and that of lime glass is around 92 l0 While the coefficient of expansion of the above-described bonding material is somewhat different from that of lead and lime glasses, and while the coefiicient of expansion of these materials may vary with the temperature, I have found that after heating up to 500 C. or above and during cooling the assembly down to room temperature, the bond is free from any tendency to craze and crack and that a durable firm bond and a secure seal are obtained between the glass elements. The elasticity of the bond material above described compensates for irregularities in expansion within the material itself and for slight differences in coefficients of expansion between the glass of the bulb and button parts, and this characteristic of the bonding material is believed to be responsible at least in part for the freedom from craze and cracks in the joint formed between the glass elements. These and other characteristics of the bond contribute to its tensile strength and to the quality of forming a substantially integral. bond 3. 1 between the abutting Surfaces of the bulb and button parts.

The bonding and sealing material when thus fused between the juxtaposed and abutting surfaces of the peripheral edges forms a firm union between the soft glass elements, which has been demonstrated by tests to be at least as strong, if not stronger, than the glass itself. This fused bonding material appears to merge into and in effect form an integral part of the glass of the elements, though the bonding operation is carried on at a temperature well below the softening temperature of the glass, and with the film or layer of bond having tensile strength adequate not only to firmly unit the elements when the lamp is evacuated but also when the lamp is pressurized with gas. With the preferred bonding material, the layer approaches molecular depth at the pressure points with a variation in thickness of the layer to compensate for the irregularities in the abutting surf-aces and also forms a firm and secure bond between the leading in means and the button material.

These important features, together with the important features and advantages previously set forth, greatly facilitate the manufacturing of incandescent lamps and enable the production of lamps at a materially reduced cost. Moreover, it is possible with this invention to eliminate the conventional base, as well as to produce lamps having very short light-center lengths and which can be accuratel controlled in the manufacture of the lamp. Furthermore, with the tubular terminal construction which I have illustrated, conventional pumping methods can be eliminated,

and the envelope can be thoroughly purged of residual gas in a much shorter time than with conventional pumping processes with which I am familiar, and the envelope can be filled and sealed at much higher envelope pressures.

What is claimed is:

1. A miniature incandescent lamp comprising a glass bulb having an opening therein, a glass button part sealed in said opening, a filament in said lamp, and support wires connected with said filament and extending through said button part and hermetically sealed thereto, and transverse members secured to each support wire at predetermined distances from the filament to facilitate positioning of the filament relative to the button part when said support wires are sealed in said button part.

2. In a miniature incandescent lamp having a glass bulb part having a neck-like opening therein and an electric filament in said bulb, means for supporting and aligning said filament in said bulb comprising a button part having means on the edge thereof for cooperating with the opening'in said bulb to facilitate alignment of the button part relative to the bulb, and filament support wires extending through said button having transverse members fastened thereto at predetermined distances from the filament to facilitate alignment of the filament relative to the button part when the support wires are sealed therein glass bulb part having a neck-like opening therein, a filament in said lamp, and leading-in wires for supporting said filament on their inner ends and extending outwardly through said opening, and means for closing said opening comprising a glass tube having an outwardly flared portion on one end thereof with said flanged portion closely fitting said opening and having notches in the edge thereof through which the leading-in wires pass, and means for sealing said flange and support wires to said bulb comprising a low temperature adhesive having a melting point below the softening point of the flange and bulb parts,

all)

by bringing said transverse members into contact with the surface of the button part before effecting the seal.

3. A miniature incandescent/lamp comprising a said glass tube providing a tipping oif means for said bulb.

4. The method of making an incandescent lamp mount comprising forming a button part of insulating material with at least two openings therein for the reception of leading in wires to support a filament within the lamp, fastening a short metallic member to each leading inwire in transverse relationship thereto and at a predetermined distan'ce from one end thereof, forming a bead of sealing material about the metallic member on each leading in wire, inserting the leading in wires through the openings in the button part, heating the beads of sealing material while exerting a slight longitudinal pressure on the leading in wires whereupon the sealing material will fill the openings to seal the wires therein with the transverse members restinglightly against one surface of the button part to acourately the distance of said one end of the leading in wires relative to the button part and then securing a filament to said one end of the leading in wires.

5. The method of making an incandescent lamp mount comprising forming a button part of insulating material with at least two openings thereinfor the reception of leading in wires to support a filament within the lamp, fastening a short metallic member to each leading in wire in transverse relationship thereto and at .a predetermined distance from one end thereof, inserting the leading in wires through the openings in the button part with the transverse members in meeting engagement with one surface thereof and sealing the leading in wires in said openings.

REGINALD K. BRAUNSDORFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

